\\[-1.8ex] Soil Heterogeneity & $-$0.044$^{**}$ & $-$0.042$^{*}$ & $-$0.047$^{**}$ & $-$0.042$^{*}$ \\ 
  & (0.022) & (0.022) & (0.021) & (0.021) \\ 
\\[-1.8ex] 
Observations & 23,431 & 23,431 & 23,158 & 23,158 \\ 
R$^{2}$ & 0.813 & 0.814 & 0.818 & 0.821 \\ 
